1. Field of the Invention
The present invention relates to a printing apparatus, a printing method, and a program, all of which enable an image to be printed on a printing medium using pigment and dye inks in the same color for at least one color on the basis of a print mode including at least a double side print mode in which both sides of a printing medium are printed.
The present invention is applicable to any equipment using various printing materials such as paper, leather, non-woven cloths, and metal. Specific applied equipment may include office equipment such as a printer, a copier, or a facsimile machine, or industrial production equipment.
2. Description of the Related Art
An ink jet printing system prints on a printing material by ejecting small droplets of ink to the printing material using any ink ejecting system such as an electrostatic suction system by applying high voltage, a system for mechanically vibrating or displacing ink (coloring ink) using a piezoelectric element or a system utilizing pressure generated when the ink bubbles as a result of heating. This printing system has the advantages of reducing noise generated during printing and increasing a resolution and a printing speed using a print head having densely integrated ink ejection openings. Printing apparatuses employing such an ink jet printing system are common in typical homes. The volume of domestic printing tends to increase. This is because the printing apparatus exhibits high performance sufficient to easily print photographs as beautiful as or more beautiful than silver halide photographs and because personal computers are common. Another reason is that more users use a home printing apparatus (printer) to print New Year's cards and browse and print Web pages with the improved Internet environment.
With such an increase in print volume, proportion of print cost in users' consumption increases. Accordingly, it has been more and more desirable to reduce print cost. Thus, there is a gradually growing demand for a printing apparatus that can reduce the used printing materials to half by printing both sides of the printing material (double side printing). Double side printing can also be effectively used for letter printing, a typical example of printing by general user.
An example of a patent document disclosing the double side print mode is Japanese Patent Application Laid-open No. 7-314734 (1995). Japanese Patent Application Laid-open No. 7-314734 (1995) has been proposed as measures for suppressing a show-through phenomenon that may occur during the double side printing, in which both sides of a printing medium are printed. Specifically, the show-through phenomenon is suppressed by reducing a print density in the double side print mode compared to a single side print mode.
Presently, an ink mainly composed of dye-based components (hereinafter referred to as a “dye ink”) is considered to be more advantageously used to print an image having a photographic quality on an exclusive sheet such as surface treated coated paper. The dye ink can be generated by dissolving variable water-soluble dyes in water or a mixture of water and an organic solvent. However, the dye ink tends to exhibit a low print grade for ordinary paper. Accordingly, it is not suited for printing simple documents or Web pages, routinely used by users, on ordinary paper. This is because the dye of the dye ink is prone to permeate deep through fibers in the ordinary paper.
There is also a growing demand for improvement of the print grade for the ordinary paper, which is inexpensive. An ink mainly composed of pigment-based components (hereinafter referred to as a “pigment ink”) exhibits a high print grade for the ordinary paper. The pigment ink can be generated by dissolving, in a water-soluble solvent, a pigment fluid dispersion composed of a pigment dispersed in a polymer dispersant. The pigment ink is advantageous in the print grade for the ordinary paper because grains of the coloring material are larger than those in the dye and thus do not easily permeate deep through the fibers in the ordinary paper but are likely to be collected in a front layer of the ordinary paper.
Presently, ink jet printing apparatuses are commercially available which use both the dye ink and the pigment ink in order to print images having a photographic quality, while improving the print grade for the ordinary paper. Many such ink jet printing apparatuses use the pigment ink as a black ink and the dye inks as color inks (cyan, magenta, and yellow inks including those with different ink densities).
As previously described, the pigment ink exhibits a higher print grade for the ordinary paper because the grains of the coloring material are larger than those in the dye and thus do not easily permeate deep through the fibers in the ordinary paper but are likely to be collected in a front layer of the ordinary paper. Thus, if the pigment ink is used to print an image, the resulting image has a high reflection density. Further, the pigment ink also does not permeate through the periphery of the printed image. This allows the boundary of the image and a character to be clearly printed. On the other hand, the grains of the coloring material of the pigment ink, which are larger than those in the dye ink, are settled near the front surface of the printed material. The pigment ink is easily rubbed off from the printed material even by slight friction. The probability that pigment molecules are present near the front surface of the printed material is increased, thus degrading abrasion resistance.
The degraded abrasion resistance of the pigment ink is particularly problematic if double side printing is executed on various printing materials including letters. This is because the double side printing involves a process of printing an image on one side of the printing material inside a printing apparatus, then turning the printing material upside down, and subsequently passing the printing material through the printing apparatus in order to print an image on the other side. During such double side printing, a portion printed using the pigment ink, having the degraded abrasion resistance, may be transferred to an internal part of the printing apparatus when passing through a mechanism structure part such as a conveying passage for the printing material which is provided inside the printing apparatus. The ink transferred to the internal part of the printing apparatus may adhere to contaminate the printing material. Further, when printing materials printed with images rub against each other, the pigment may simply be rubbed off to contaminate the printing materials.
To avoid the above problem, it is conceivable to reduce the amount of a black pigment ink used in a double side print mode for the double side printing. In this case, however, the decrease in the amount of the black pigment ink used reduces the optical reflection density of the printed image. Accordingly, it is conceivable to compensate for the optical reflection density by superimposing color (cyan, magenta, and yellow) dye inks on one another. However, the inventors found that the manner is not enough with respect to the following.
That is, compared to the black pigment ink, an insufficient optical reflection density results from a process black, expressed by superimposing the color (cyan, magenta, and yellow) dye inks on one another. Therefore, even if the amount of black pigment ink used in the double side print mode is reduced and an attempt is made to compensate for the accompanying decrease in density using the process black, the decrease cannot be sufficiently compensated for. As a result, even though the black pigment ink, exhibiting a high print grade, is used for the ordinary paper, the performance of the pigment may not be fully demonstrated, thus lowering the print grade. Moreover, when the color dye inks are superimposed on each other in order to express the process black, a large amount of ink impacts the printing material, so that the ink may permeate through the printing material to its back side to cause the show-through phenomenon. Thus, the grade of the back side of the printing material, which is to be printed next, may lower before printing or a decrease in print grade called migration may occur. These problems may dissatisfy users.